Abstract P106: SELECTIVE CYTOTOXICITY IN KRAS-MUTANT CANCER CELLS THROUGH COORDINATED STABILIZATION OF KRAS AND ITS UPSTREAM REGULATORS USING SMALL MOLECULE DRUG
Jul 2026· Cancer Research· Vol 86, pp. P106-P106· 0 citations
TL;DR
Results suggest that C1-induced lethality involves coordinated stabilization of multiple upstream KRAS regulators, with GRB2 acting as one component that may amplify signalling in a mutant-specific context, a novel mechanistic axis of synthetic lethality in KRAS-driven cancers.
Abstract
KRAS is one of the most frequently mutated oncogenes in cancer, driving tumorigenesis and resistance to therapy. However, its smooth, shallow surface and lack of deep binding pockets have historically made it difficult to target with small molecules. Our lab identified Merodantoin (C1), a small molecule that selectively induces cell death in KRAS-mutant cancer cells by hyperactivating KRAS. This activation leads to stimulation of the mTORC2–AKT signalling pathway, elevated reactive oxygen species (ROS) levels, and subsequent cell death via mitochondrial fission and mitophagy. To further elucidate the upstream mechanisms underlying KRAS hyperactivation, we employed mass spectrometry- and Western blot-based Cellular Thermal Shift Assays (MS-CETSA and WB-CETSA). In KRAS G13D mutant cells, C1 treatment resulted in thermal stabilization of KRAS, its upstream adaptor GRB2, and the prenylation enzymes Farnesyltransferase-α/β, which are essential for KRAS membrane localization and function. Functional knockdown studies showed that GRB2 silencing partially rescued both C1-induced cytotoxicity and impaired spheroid formation, suggesting a contributory—but not exclusive—role in modulating the KRAS-driven response. In KRAS wild-type cells, C1 induced minimal cell death and exhibited stability in GRB2 but not KRAS. Autophagy-inducing treatments (Rapamycin, EBSS) stabilized KRAS in mutant cells but not GRB2, and neither protein in wild-type cells, indicating that KRAS stabilization is mutation-dependent, while GRB2 stabilization is specific to C1. These results suggest that C1-induced lethality involves coordinated stabilization of multiple upstream KRAS regulators, with GRB2 acting as one component that may amplify signalling in a mutant-specific context. Together, this reveals a novel mechanistic axis of synthetic lethality in KRAS-driven cancers.
Benedict J. Leong, Kartini Iskandar, Liang Ying Yu, Shazib Pervaiz. SELECTIVE CYTOTOXICITY IN KRAS-MUTANT CANCER CELLS THROUGH COORDINATED STABILIZATION OF KRAS AND ITS UPSTREAM REGULATORS USING SMALL MOLECULE DRUG [abstract]. In: Proceedings of Frontiers in Cancer Science 2025; 2025 Nov 5-7; Singapore. Philadelphia (PA): AACR; Cancer Res 2026;86(13_Suppl):Abstract nr P106.
Alterations in KRAS are among the most common oncogenic drivers in solid tumors, including pancreatic, colorectal, and lung cancers, with G12D, G12V, and G12C representing the most frequent mutations. Unlike wild-type KRAS, which cycles between inactive and active states, mutant KRAS is constitutively active and drives uncontrolled proliferation and survival through downstream signaling. KRAS PROteolysis TArgeting Chimera (PROTAC) degraders are designed to eliminate the oncogenic protein, thereby stopping this dysregulated signaling cascade at the source. Their iterative mechanism, in which one PROTAC molecule can degrade multiple target proteins, may offer advantages over inhibitors, particularly in tumors with KRAS amplification, a common feature of KRAS-driven cancers and a resistance mechanism to inhibitor therapy. KRAS degradation may also produce deeper, more sustained pathway suppression and a distinct resistance profile compared with inhibition. Both mutation-selective and pan-KRAS PROTAC degraders have been identified and will be described herein. Both classes of PROTAC degraders target the ON and OFF forms of KRAS while sparing the related isoforms, HRAS and NRAS. ARV-806 is a PROTAC KRAS G12D-selective degrader currently being evaluated in a Phase1/2 clinical study (NCT07023731). Preclinically, ARV-806 demonstrated sub-nanomolar potency for degrading KRAS G12D and >25-fold greater anti-proliferative potency compared to inhibitors and another clinical-stage degrader. In vivo, ARV-806 induced robust KRAS G12D degradation that was sustained for >7 days after a single IV dose and produced tumor regressions across multiple models. Orally bioavailable PROTAC pan-KRAS degraders have also been identified that potently degrade common KRAS mutations like G12C/D/V, difficult-to-target variants such as G12R and Q61H, and amplified KRAS. In vitro, degradation led to potent antiproliferative activity and induction of apoptosis of KRAS-driven cells, with no observed impact on cells not driven by KRAS. In vivo, treatment with the PROTAC pan-KRAS degrader led to regressions in multiple tumor models bearing different KRAS mutations. Additionally, a sustained pharmacodynamic effect was observed with the PROTAC pan-KRAS degrader inducing prolonged suppression of KRAS protein levels and downstream signaling compared to an inhibitor. In a KRAS-mutant syngeneic model, pan-KRAS degradation combined with immune checkpoint inhibition produced more complete responses than a pan-RAS inhibitor combination, accompanied by increased cytotoxic T-cell and dendritic-cell infiltration, reduced myeloid populations, and enhanced immune checkpoint response gene signatures. Together, these findings support oral pan-KRAS degraders as a differentiated therapeutic approach for KRAS-driven cancers, with potential advantages in monotherapy activity, durability, immune engagement, and tolerability relative to pan-RAS targeting.
Kathryn D. Smith. Eliminating the oncogenic driver: Advancing targeted degradation of KRAS [abstract]. In: Proceedings of AACR Drug Discovery and Development (AACR D3) Conference; 2026 Jul 21-24; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(14_Suppl):Abstract nr IA05.
Kathryn D. Smith· Clinical Cancer Research· 0 citations
The RAS/mitogen-activated protein kinase (MAPK) pathway is a pivotal oncogenic driver in numerous malignancies, most prominently pancreatic ductal adenocarcinoma, colorectal carcinoma, non-small cell lung cancer, and melanoma. The emergence of direct KRAS inhibitors, pan-RAS inhibitors, and agents targeting downstream signaling pathways (including MEK and ERK) has profoundly reshaped the therapeutic landscape. However, durable clinical responses remain scarce, owing to profound, rapid, and adaptive resistance mechanisms that extend far beyond tumor cell-intrinsic pathways. Over the past five years, accumulating evidence has unequivocally established that the tumor microenvironment (TME)—particularly its immune components—plays a key role in driving this resistance. This review synthesizes recent advances in understanding how specific TME constituents, including immune cells, cancer-associated fibroblasts (CAFs), and the extracellular matrix (ECM), interact with tumor cells to promote escape from pathway inhibition. We examine bidirectional signaling induced by therapy, consequent tumor cell plasticity, and the formation of a protective niche. Finally, we outline rational combination strategies that simultaneously target the RAS/MAPK axis and key TME vulnerabilities, such as immunotherapy combinations, CAF reprogramming, and ECM normalization, to overcome stromal-mediated resistance and achieve deeper, more sustained clinical responses.
Wen-Hao Ma, Xing-Yu Guo, Xiu-Ting Liu· Cancer Advances· 0 citations
Kirsten rat sarcoma viral oncogene homolog (KRAS) G12C mutations represent the most common driver alterations in non-small cell lung cancer and were long considered "undruggable" due to the lack of a suitable binding pocket on the protein surface. Recent structural breakthroughs have identified the Switch-II allosteric pocket, facilitating the development and clinical application of several covalent inhibitors—including Sotorasib, Adagrasib, and Divarasib—which have substantially improved outcomes for patients harboring this mutation. However, primary and acquired resistance remain major obstacles to long-term efficacy, with resistance mechanisms involving RTK-mediated adaptive signaling reactivation, aberrant PI3K–AKT–mTOR pathway activation, secondary genetic alterations, and other factors. Moreover, intratumoral heterogeneity, characterized by the coexistence of sensitive and resistant subclones, further complicates therapeutic responses. To overcome these challenges, combination strategies have become a major research focus, including the pairing of KRAS G12C inhibitors with immune checkpoint inhibitors, RTK-targeted agents, SHP2 inhibitors, or MEK inhibitors, aiming to block escape pathways and enhance antitumor immunity. Future directions emphasize optimizing combination regimens, exploring personalized immunotherapy, and developing next‑generation inhibitors to prolong survival. This review systematically summarizes the molecular mechanisms driving KRAS G12C‑mutant lung cancer, clinical applications of targeted drugs, resistance and heterogeneity challenges, and progress in combination therapy, providing a reference for clinical decision‑making and further research in this field.
Xizhi Zha· Theoretical and Natural Scie...· 0 citations
BACKGROUND
KRAS is a central oncogenic driver in multiple solid malignancies, including non-small cell lung cancer, pancreatic ductal adenocarcinoma, and colorectal cancer. Activating KRAS mutations, together with co-mutations and gene-dosage alterations, reprogram signaling pathways, cellular metabolism, and the tumor microenvironment, thereby promoting aggressive tumor behavior and therapeutic resistance. Despite recent advances, including KRAS G12C inhibitors and emerging agents targeting G12D, pan-RAS(ON), and nucleotide-free RAS, clinical responses remain limited in many KRAS-mutant contexts due to rapid and multifaceted resistance.
AIM OF REVIEW
This review aims to examine the mechanisms underlying resistance to KRAS-targeted therapies and to provide an integrated perspective on how adaptive tumor responses limit the durability of KRAS inhibition.
KEY SCIENTIFIC CONCEPTS OF REVIEW
Selective pressure from KRAS-targeted therapies drives adaptive tumor evolution through on-target alterations, rewiring of signaling networks, and non-genetic changes in cell state and the tumor microenvironment. This review synthesizes current knowledge on these resistance mechanisms and highlights emerging therapeutic strategies, including rational combination approaches, enhanced RAS pathway suppression, targeted protein degradation, and KRAS-directed immunotherapies. By integrating recent preclinical and clinical advances, this work provides a comprehensive framework for understanding resistance and improving the durability of KRAS pathway inhibition in cancer.
Rawan Salih, F. Sirajudeen, Mohamed Rahmani· Journal of Advanced Research· 0 citations
Gain-of-function mutations in RAS genes are the most prevalent oncogenic mutations responsible for about one-third of all human malignancies. Despite decades of research, direct targeting of RAS remains a major clinical challenge, as FDA-approved RAS inhibitors and those in clinical trials have limited efficacy and on-target toxicities. We recently characterized a mechanistically distinct pan-RAS inhibitor, ADT-007, with highly potent and selective growth-inhibitory activity against cancer cells with mutant or activated RAS (Cancer Res, 2025). Cellular, biochemical, and biophysical studies demonstrated that ADT-007 binds nucleotide-free RAS, blocking GTP loading and RAS activation, leading to mitotic arrest and apoptosis. Notably, ADT-007 induced apoptosis and caused near-complete inhibition of colony formation in KRAS mutant pancreatic cancer cells, whereas the pan-KRAS inhibitor, BI-2865, and the pan-RAS inhibitor, RMC-6236, did not induce apoptosis and marginally inhibited colony formation when tested under the same conditions at 10x growth IC50 values. In addition, KRAS mutant cancer cell lines did not develop resistance to ADT-007 under chronic exposure, in contrast to BI-2865 and RMC-6236, which readily produced cultures that were essentially unresponsive to the inhibitor that induced resistance. Interestingly, the RMC-6236-resistant cells exhibited cross-resistance to BI-2865 and vice versa, as well as cross-resistance to allele-specific KRAS inhibitors, but not to ADT-007. The RAS selectivity of ADT-007 involves a unique metabolic mechanism of deactivation by UDP-glucuronosyltransferases (UGTs), which are expressed in normal cells but not in KRAS-mutant cancer cells. An orally bioavailable prodrug of ADT-007, ADT-1004, demonstrated favorable tolerability and suppressed tumor growth in orthotopic and patient-derived xenograft models of pancreatic cancer, accompanied by reductions in activated RAS and p-ERK levels (Mol Cancer, 2025). ADT-1004 displayed superior efficacy compared with sotorasib or adagrasib in a xenograft model using a resistant pancreatic cancer cell line. These findings support the further development of ADT-1004, which holds promise for broad and durable efficacy against RAS-driven cancers, with the potential to overcome resistance and on-target toxicities.
Junwei Wang, Xi Chen, Bandi D. S. Reddy, Ganji P. Nagaraju, Sindhu Ramesh, Austin Moore, Thomas Holmes, Kristy L. Berry, Khalda Fadlalla, Elmar Nurmemmedov, Ivan Babic, Jeremy B. Foote, Donald J. Buchsbaum, Asfar S. Azmi, Yulia Y. Maxuitenko, Adam B. Keeton, Bassel F. El-Rayes, Gary A. Piazza. ADT-1004: A mechanistically distinct pan-RAS inhibitor with the potential to escape resistance and mitigate on-target toxicities that limit efficacy and safety of other RAS inhibitors [abstract]. In: Proceedings of AACR Drug Discovery and Development (AACR D3) Conference; 2026 Jul 21-24; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(14_Suppl):Abstract nr A089.
Junwei Wang, Xi Chen, Bandi D. S. Reddy et al.· Clinical Cancer Research· 0 citations
These breakthroughs have validated direct KRAS inhibition as an effective therapeutic strategy, however, durable clinical responses remain limited by intrinsic and acquired resistance, pathway reactivation, tumour heterogeneity, and the lack of effective therapies for non-G12C KRAS mutations.
Pasham Uma, Dandotikar Neha, R. Manisha et al.· International Journal of Inn...· 0 citations